The issue is that they interfere with each other in the fringe areas of coverage. Were they to, each, increase power the local coverage of both would be impaired.I find it perplexing that some AM stations in Cleveland reduce power so significantly at night so as to not interfere with stations hundreds of miles away, yet they don't even cover Cuyahoga County.
Those stations like 1260 and 1300 were licensed post-WW II and have to protect senior stations on the channels.
Ones like 1420, 850 and 1220 served Cleveland well when the city had not grown outwards; Cleveland Heights was "way out there" and Parma was separated from Cleveland by fields and farms. But the city grew, and the signals did not and could not.
1490 was a suburban station intended to serve Cleveland and Shaker Heights and that area. 1540 was a daytimer serving the growing Black community.
There is no solution. Nationally, in the 100 biggest markets there are just about 180 AM stations that cover at least 80% of the market day and night. Some markets have none, in fact.